[14] RFR 8230765: Implement nmethod barrier for x86_32 platforms

[Zhengyu Gu]

Hi Erik,

On 11/26/19 8:24 AM, Zhengyu Gu wrote:
>> Here is a patch with my proposed cleanup:
>> http://cr.openjdk.java.net/~eosterlund/8230765/webrev.02/
>>
>> Incremental:
>> http://cr.openjdk.java.net/~eosterlund/8230765/webrev.01_02/
>>
> 
> Yes, this indeed a much cleaner approach. I will take your proposed 
> cleanup and run through submit.

I took your patch. There is just one little hiccup: compiler expects 
intptr_t instead of int* on x86_32, the fix is straightforward.

    __ push(tmp);
-  __ movptr(tmp, bs_nm->disarmed_value_address());
+  __ movptr(tmp, (intptr_t)bs_nm->disarmed_value_address());
    Address disarmed_addr(tmp, 0);
    __ align(4);
    __ cmpl(disarmed_addr, 0);


Full webrev: http://cr.openjdk.java.net/~zgu/JDK-8230765/webrev.02/

and patch passed submit tests.

Okay to push?

Thanks,

-Zhengyu


> 
> -Zhengyu
> 
> 
>> Thanks,
>> /Erik
>>
>> On 11/25/19 9:35 PM, Zhengyu Gu wrote:
>>> Hi all,
>>>
>>> Please review this implementation of nmethod barrier for x86_32 
>>> platforms.
>>>
>>> x86_32 implementation mirrors x86_64's. The only difference is where 
>>> it reads nmethod disarmed value.
>>>
>>> Unlike 64-bits, 32-bits platform does not have a dedicated register 
>>> for current thread. So that it is cheaper to read disarmed value from 
>>> global location than from per-thread GC data.
>>>
>>> Currently, only Shenandoah GC uses the implementation for its 
>>> concurrent class unloading. This implementation, along with 
>>> Shenandoah concurrent class unloading, has been baked in 
>>> shenandoah/jdk repo for some time now,  they are ready for integration.
>>>
>>>
>>> Bug: https://bugs.openjdk.java.net/browse/JDK-8230765
>>> Webrev: http://cr.openjdk.java.net/~zgu/JDK-8230765/webrev.01/
>>>
>>>
>>> Test:
>>>   hotspot_gc with x86_64 and x86_32 JVM on Linux
>>>   Submit test.
>>>
>>> Thanks,
>>>
>>> -Zhengyu
>>>
>>